On a custom board, consisting in an Atmega328P and some few passives, I want to check the current consumption of the board in Power Down mode. The only pull-up resistor is the 10k one for the reset circuit. Then there are a number of de-coupling capacitors, that's all. No external crystal used. The atmega is running at 8 MHz internal RC clock, 3.3VDC, BOD disabled.

I've picked some ideas from this post:http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1285656727/5

So I've created a very simple sketch that puts the atmega in Power Down State:

The issue is that I was hopping to see some few microamps entering the board but I'm finally monitoring 105 uA after entering the Power Down state. Being the circuit so simple I wonder whether I'm entering the low-power state and disabling the functions correctly... On the other hand, I'm now checking the possible leakage through the de-coupling capacitors.

Bit 0 - PRADC: Power Reduction ADCWriting a logic one to this bit shuts down the ADC. The ADC must be disabled before shut down.The analog comparator cannot use the ADC input MUX when the ADC is shut down.

Bit 0 - PRADC: Power Reduction ADCWriting a logic one to this bit shuts down the ADC. The ADC must be disabled before shut down.The analog comparator cannot use the ADC input MUX when the ADC is shut down.

But, if we don't enable the ADC at the 1st place, we don't have to do the above setting right?Look at 9.10.1 of the datasheet.

I've investigated the possibility of "loosing" current through the decoupling capacitors but, even in the worst cases, they might be wasting a total of a few uAmps maximum. I think I'm going to order a couple of DIP-form atmegas in order to do the tests on a breadboard. Then I'll be able to mount only the essential components and measure the current consumption. That will let me discard any programming-related problem.

I think Atmel calls them "asynchronous interrupts". Off the top of my head (read that as probably with mistakes): pin-change interrupts, USART activity, TWI address match, watchdog interrupt, INTx level. For the 328, the table in "9.1 Sleep Modes" provides a good overview.